1. Field
The present invention relates to an organic light emitting diode display and a manufacturing method thereof.
2. Description of the Related Art
An organic light emitting diode (OLED) display includes a plurality of OLEDs formed of a hole injection electrode, an organic emission layer, and an electron injection electrode. Each organic light emitting diode emits light by energy generated when excitons generated as electrons and holes are combined and drop from an excited state to a ground state, and the OLED display displays an image by using the light.
The organic light emitting element may be deteriorated by external factors such as external moisture, oxygen, or ultraviolet rays (UV) so packaging methods for encapsulating the organic light emitting element are important, and the organic light emitting diode (OLED) display is required to be manufactured thin or flexible for various types of applications. In order to encapsulate the organic light emitting element and form a thin organic light emitting diode (OLED) display and bend it, a thin film encapsulation (TFE) method has been developed. In the thin film encapsulation method, a display area is covered with a thin film encapsulation layer by alternately stacking an inorganic layer and an organic layer over the organic light emitting elements that are formed in the display area of the display substrate. When the display substrate of the organic light emitting diode (OLED) display including the thin film encapsulation layer is formed with a flexible film such as polyimide (PI), it can be easily bent and advantageously be made slim.
When the flexible organic light emitting diode display is bent, stress occurs. Specifically, tensile stress occurs on a convex outside surface and compressive stress occurs on a concave inside surface. A neutral plane NP at which no force occurs is present in an intermediate region between the outside and the inside surfaces. A picture abnormality does not occur in the organic light emitting diode display only when the organic light emitting element is positioned in the neutral plane.
However, when the thickness of the organic light emitting diode display is increased because of additional internal and external films such as a polarizing film and a passivation film attached to the organic light emitting diode display, the tensile stress and the compressive stress are increased and the neutral plane becomes narrow. Accordingly, it is difficult to position the organic light emitting element in the neutral plane. Further, since the organic light emitting diode display has a layered structure made of complex materials, asymmetry of strains occur due to a difference in tensile stress and compressive stress of the outside surface and the inside surface of a bent bending portion. Accordingly, it is difficult to position the organic light emitting element in the neutral plane, and thus picture abnormality occurs.
The above information disclosed in this Background section is only for enhancement of an understanding of the background of the invention and therefore it may contain information that does not form prior art that is already known to a person of ordinary skill in the art.